Yaskawa A1000 SC Fault — What It Means
The SC fault on a Yaskawa A1000 VFD indicates a short circuit in the drive’s output stage. The drive has detected a short between the output terminals (U, V, W) or within the internal power module (IGBTs). This is a critical hardware failure where the IGBTs are conducting improperly or have physically shorted, creating a direct current path. The drive immediately stops output and trips the alarm to protect itself and downstream equipment.
This fault represents a failure in the drive’s ability to safely control current flow to the motor. The protection circuit cannot interrupt the short, so the drive shuts down completely. The fault can originate inside the drive or in the external wiring and motor.
Before You Replace Anything
Technicians sometimes replace the entire drive without first disconnecting the motor and cables to test them. A simple resistance check of the motor windings and output cables can reveal that the short is external, saving the cost of a new drive.
Common Causes
- Internal power module (IGBT) failure (~60%) The IGBTs inside the drive’s power module have physically shorted due to aging, thermal stress, voltage spikes, or manufacturing defects.
- Motor winding failure (~15%) The motor windings have shorted internally, either phase-to-phase or phase-to-ground, creating a fault the drive detects as a short circuit.
- External output cable short (~10%) A short circuit exists in the cables running from the drive to the motor, with U, V, or W wires touching each other or ground.
- Contamination or moisture inside the drive (~10%) Excessive conductive dust, metal particles, or moisture has created a short between output terminals or on the power board.
- Failed diodes or braking circuit (~5%) A short in the output rectifier diodes or the braking circuitry (if installed) is triggering the short-circuit detection.
Quick Diagnosis
Answer these to narrow it down fast.
With power off and output cables disconnected, do the U-V, V-W, and U-W terminals on the drive measure near 0 ohms (shorted)?
No: The short is likely external. Proceed to test the motor and cables.
With cables disconnected from the drive, do the motor windings measure near 0 ohms between any two phases?
No: Check the output cables for damage or shorts. If cables and motor are good, the drive has an internal fault.
Are there signs of moisture, dust, or contamination inside the drive enclosure?
No: The fault is a hardware failure in the drive's power module or protection circuit. Professional repair or replacement is required.
Step-by-Step Fix
- Remove all power to the drive, including control power and DC bus connections. Lock out and tag out the main disconnect.
- Wait for the DC bus to discharge completely (typically 5 to 10 minutes) until the display is dark and the bus voltage measures 0V with a multimeter.
- Disconnect the output cables (U, V, W) from the drive terminals.
- Measure resistance between U-V, V-W, and U-W at the motor terminal box using a multimeter. If any pair reads near 0 ohms, the motor or cables are shorted.
- Inspect the cables for physical damage, pinching, chafing, or water ingress. Replace damaged cables.
- Measure resistance between the drive’s U, V, and W terminals (with cables still disconnected). If any pair reads near 0 ohms, the drive’s internal power module has failed.
- If the drive is faulty, replace the drive or contact Yaskawa for power module replacement. If the motor or cables are faulty, repair or replace them, then reconnect and test the system.
Parts Often Needed
| Part | Notes |
|---|---|
| Yaskawa A1000 replacement drive (same model and horsepower) | Amazon | Match the exact model number and voltage rating on the drive nameplate. |
| Motor output cables (3-phase shielded cable, sized per motor horsepower) | Amazon | Use manufacturer-recommended cable type and gauge. Consult your model’s table for wire sizing. |
When to Call a Pro
Call a qualified electrician or industrial automation technician immediately. The SC fault indicates a short circuit in high-voltage power electronics or the motor circuit. Diagnosing this fault requires safely discharging the DC bus, measuring IGBT components, and working with three-phase power systems. Incorrect testing can damage the drive further or cause electric shock. If the power module has failed, replacement requires matching the exact drive model, programming drive parameters, and verifying motor compatibility. A technician will isolate whether the fault is in the drive, the motor, or the wiring, and perform the necessary repairs or replacements to restore safe operation.
Rough cost: A pro service call runs about $800-2500.